The present invention relates to a new block copolymer. More particularly, it relates to a block copolymer in which an ethylene-propylene copolymer is bonded to a polymethacrylate ester.
The living polymerization is useful for the production of monodisperse polymers and block copolymers of uniform composition, and many attempts have been made for the production of olefin block copolymers by living polymerization also in the area of coordinate polymerization that employs a Ziegler-Natta catalyst. However, it is difficult to produce block copolymers of uniform composition by living polymerization because chain transfer reactions and termination reactions take place frequently during living polymerization.
The present inventors found that a catalyst composed of V(acetylacetonate).sub.3 and Al(C.sub.2 H.sub.5).sub.2 Cl provides nearly monodisperse living polypropylene. [Makromol. Chem., 180, 1359 (1979); and Makromolecules., 12, 814 (1979)] The present inventors also found that this technology can be applied to the living copolymerization of ethylene and propylene. According to this technology, it is possible to produce a nearly monodisperse random living copolymer of ethylene and propylene. If this copolymer is copolymerized with methacrylate ester, there is obtained a block copolymer of uniform composition which is composed of the segments of nearly monodisperse ethylene-propylene random copolymer and the segments of nearly monodisperse polymethacrylate ester. The present invention was completed based on this finding.
The gist of this invention resides in a block copolymer having a number-average molecular weight of about 1,000 to about 600,000 in which the random copolymer segment (A) is bonded to the polymer segment (B), with the ratio of (A) to (B) being 15/85 to 97/3 by weight, said random copolymer segment (A) being composed of the constitutional units represented by the formulas I and II below. ##STR1## [the amount of I being 30 to 80 wt% and the amount of II being 70 to 20 wt%], said polymer segment (B) being composed of the constitutional units, represented by the formula below. ##STR2## (where R denotes a hydrocarbon group.)
Said block copolymer is produced by either of the following processes. (Process I) At first, the living polymerization of ethylene and propylene is performed in the presence of .beta.-diketone vanadium chelate and an organoaluminum compound to give a living ethylene-propylene random copolymer. Then, a methacrylate ester is polymerized in the presence of the living copolymer. (Process II) The living ethylene-propylene random copolymer is brought into contact with a halogen to halogenate the terminals of the copolymer. The halogenated copolymer is then brought into contact with metallic magnesium, and the resulting product is finally brought into contact with a methacrylate ester to perform living polymerization.
The living ethylene-propylene random copolymer is produced by copolymerizing ethylene and propylene in the presence of a polymerization catalyst composed of .beta.-diketone vanadium chelate (referred to as vanadium compound hereinafter) and an organoaluminum compound.
The vanadium compound is represented by the formula below. ##STR3## (where R.sup.1 and R.sup.2 are the same or different alkyl groups or aryl groups.) It includes, for example V(acetylacetonate).sub.3, V(benzoylacetylacetonate).sub.3, and V(dibenzoylmethanate).sub.3.
The organoaluminum compound is represented by the formula R.sub.2 AlX (where R is an alkyl group or aryl group having 1 to 8 carbon atoms, and X is a halogen atom). It includes, for example, dimethylaluminum chloride, diethylaluminum chloride, diethylaluminum bromide, and diisobutylaluminum chloride.
The polymerization reaction should preferably be performed in a solvent which is inert and liquid at the time of polymerization. Examples of the solvent include saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; saturated alicyclic hydrocarbons such as cyclopropane and cyclohexane; and aromatic hydrocarbons such as benzene, toluene, and xylene.
Ethylene and propylene can be brought into contact with the polymerization catalyst in any manner. Preferably, the contact is accomplished by adding a solution of the organoaluminum compound and then a solution of the vanadium compound to a solvent solution of ethylene and propylene.
The amounts of the polymerization catalyst used for 1 mol of ethylene and propylene are as follows: The amount of vanadium compound is 1.times.10.sup.-4 to 0.01 mol, preferably 5.times.10.sup.-4 to 5.times.10.sup.-3 mol, and the amount of the organoaluminum compound is 1.times.10.sup.-3 to 0.1 mol, preferably 5.times.10.sup.-3 to 0.01 mol. Preferably, the organoaluminum compound is used in an amount of 5 to 25 mol for 1 mol of the vanadium compound.
The molecular weight and yields of the living copolymer can be regulated by changing the reaction temperature and reaction time. According to this invention, it is possible to produce a polymer which has a molecular weight distribution similar to that of a monodisperse polymer, if the polymerization temperature is kept low, particularly lower than -50.degree. C. Polymerization at -65.degree. C. or below provides a living ethylene-propylene random copolymer having a molecular weight distribution of 1.05 to 1.40 which is defined by Mw/Mn (where Mw is the weight-average molecular weight and Mn is the number-average molecular weight).
The polymerization reaction may be accompanied by a reaction accelerator such as anisole, water, oxygen, alcohol (methanol, ethanol, isopropanol, etc.), and ester (ethyl benzoate, ethyl acetate, etc.). The reaction accelerator is used in an amount of 0.1 to 2 mol for 1 mol of the vanadium compound.
The ratio of ethylene to propylene in the living copolymer should be in such a range that the property of the final block copolymer attributable to the ethylene-propylene random copolymer in it is not adversely affected. The ethylene-to-propylene ratio is usually 30/70 to 80/20 by weight.
The composition of the ethylene-propylene random copolymer can be regulated by changing the ratio of ethylene to propylene at the time of living copolymerization. The greater the amount of ethylene used, the broader the molecular weight distribution of the resulting polymer, and this is not preferable. A living copolymer of high ethylene content having a narrow molecular weight distribution (or a nearly monodisperse living copolymer) can be produced by performing living polymerization of a small amount of propylene prior to the living copolymerization of ethylene and propylene. The living copolymer obtained in this way has a narrow molecular weight distribution and yet contains a large amount of ethylene. In actual, propylene alone is supplied at first to the polymerization system so that living polypropylene having a number-average molecular weight of 500 to 2000 is formed. Subsequently, ethylene is supplied to continue living polymerization in the presence of a large amount of unreacted propylene monomer until the random copolymerization of ethylene and propylene is completed.
In the way mentioned above, it is possible to produce a nearly monodisperse living ethylene-propylene random copolymer having a number-average molecular weight of about 500 to about 500,000 (in terms of propylene, to be repeated hereinafter).
In the next step, a methacrylate ester is polymerized in the presence of the random copolymer to give the block copolymer of this invention. (Process I).
The methacrylate ester is represented by the formula below. ##STR4## (where R denotes a hydrocarbon group having 1 to 20 carbon atoms.) Preferred examples of R are alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl groups.
The polymerization of methacrylate ester is accomplished by bringing the methacrylate ester into contact with the living ethylene-propylene random copolymer. The polymerization of methacrylate ester is carried out usually at 0.degree. C. to 50.degree. C. The reaction rate is slow at a temperature below -50.degree. C. which is preferable for the living copolymerization of ethylene and propylene. According to the preferred polymerization process, the living copolymerization of ethylene and propylene is carried out for a prescribed period of time, and then the methacrylate ester is added while keeping the polymerization temperature. Finally, the reaction temperature is raised to effect the polymerization of the methacrylate ester.
The molecular weight of the polymethacrylate ester can be regulated by changing the polymerization temperature and polymerization time. If the polymerization temperature is excessively high, the resultant living polymethacrylate ester has a broad molecular weight distribution. Thus the preferred polymerization temperature is 0.degree. C. to 30.degree. C. The molecular weight increases in proportion to the polymerization time until it reaches a certain magnitude which is about 10,000 to about 20,000. Therefore, process I is suitable for the production of living polymethacrylate ester having a number average-molecular weight of about 500 to 5,000.
If it is desirable to increase the molecular weight further, the above-mentioned process II should be used. According to this process, the living ethylene-propylene random copolymer is brought into contact with a halogen, and the resulting product is brought into contact with metallic magnesium and the reaction product is finally brought into contact with a methacrylate ester.
When the living ethylene-propylene random copolymer is brought into contact with a halogen, the copolymerization of ethylene with propylene is suspended immediately. The resulting product is an end-halogenated ethylene-propylene random copolymer having the skeleton of the above-mentioned living ethylene-propylene random copolymer.
The halogen that can be used in that step is iodine, chlorine, or bromine, and it is used in an amount of 2 mol and up, preferably 2 to 5 mol, for 1 mol of the organoaluminum compound used for the production of ethylene-propylene random copolymer. The halogen may be used as such; but it should preferably be used in the form of solution in the same solvent as used for the production of the above-mentioned random copolymer. The concentration of the solution is 0.1 to 5 mol in 1 liter of the solvent. Usually, the halogenation reaction is performed for 5 minutes to 6 hours at -50.degree. to -100.degree. C. Upon addition of an alcohol to the reaction system, the halogenated ethylene-propylene random copolymer separates out.
The halogenated ethylene-propylene random copolymer thus obtained is then brought into contact with metallic magnesium. To achieve the contact, the halogenated copolymer should be dissolved in tetrahydrofuran or diethylether. The contact is carried out at the refluxing temperature of the ether solvent for 1 to 10 hours. The ratio of the halogenated copolymer to the metallic magnesium is usually 1000/1 to 10/1 by weight.
To the reaction solution thus obtained is added a methacrylate ester to effect the living polymerization of the methacrylate ester. Thus there is obtained the block copolymer of this invention. The methacrylate ester is used in an amount more than 10 times (by weight), preferably more than 20 times the amount of the halogenated ethylene-propylene random copolymer. The living polymerization of methacrylate ester should preferably be performed at a low temperature as in the case of living copolymerization of ethylene and propylen. The lower the polymerization temperature, the narrower the molecular weight distribution of the resulting polymer. If the reaction temperature is excessively low, the polymerization rate is slow. Thus the polymerization temperature from -50.degree. C. to -100.degree. C. is recommended.
The molecular weight of the living polymer can be regulated by changing the polymerization time. The longer the polymerization time, the greater the molecular weight. It is also possible to increase the molecular weight by increasing the polymerization temperature; but the polymerization at a high temperature results in a broad molecular weight distribution and consequently is not desirable. Process II provides a living polymethacrylate ester having a much higher molecular weight than process I does. According to process II, it is even possible to produce a living polymethacrylate ester having a number-average molecular weight of about 100,000.
The polymerization of methacrylate ester in process I and process II is suspended when an alcohol is added to the polymerization system, and at the same time the resulting block copolymer separates out. The block copolymer is separated from excess methacrylate ester and then washed with acetone, methanol, or the like, followed by drying, for recovery.
In this way there is obtained an AB-type block copolymer in which the copolymer segment (A) of narrow molecular weight distribution formed by random copolymerization of ethylene and propylene is connected to the polymer segment (B) of narrow molecular weight distribution formed by polymerization of methacrylate ester. The copolymer of this invention usually has a number-average molecular weight of about 1,000 to about 600,000, preferably 3,000 to 200,000, more preferably 5,000 to 100,000. The ratio of segment (A) to segment (B) is 15/85 to 97/3 (by weight).
The molecular weight and composition of the block copolymer can be regulated by changing the molecular weight and composition of the living ethylene-propylene random copolymer and the conditions for polymerization of methacrylate ester.
The block copolymer of this invention is characterized by that it is a nearly monodisperse polymer of uniform composition having a molecular weight distribution (Mw/Mn) of 1.05 to 1.40.
The block copolymer of this invention is composed of nonpolar polymer segments (A) and polar polymer segments (B). Therefore, it differs in properties from the conventional block copolymers and polymer mixtures. It is useful as a dyeing agent, adhesive, polymer modifier, compatibilizing agent, and surface modifier.
The invention is now described in more detail with reference to the following examples, in which the characterization of polymers and copolymwers was carried out in the following way.
Molecular weight and molecular weight distribution: Determined by using GPC (gel permeation chromatography), Model 150, made by Waters Co. under the following conditions.
Solvent: trichlorobenzene.
Temperature: 135.degree. C.
Flow rate of solvent: 1.0 ml/min.
Sample of concentration: 0.15 wt/vol%.
Column: GMH6 made by Toyo Soda Kogyo Co. The calibration curve of polypropylene for determination was prepared according to the universal method from the calibration curve of polystyrene obtaine dby using the standard sample of monodisperse polystyrene available from Waters Co.
Determination of polymer structure (.sup.13 C-NMR spectrum): Performed by using Model XL-200 made by Varian Co., equipped with the PFT pulse Fourier transformer
Frequency: 50 MHz.
Temperature: 120.degree. C.
Pulse width: 8.2 .mu.s .pi./3.
Pulse interval: 4 sec.
Number of integration: 5000.
Sample: prepared by dissolving in a 2:1 mixture solvent of trichlorobenzene and heavy benzene.
Infrared absorption spectrum: Determined by using an infrared spectrophotometer, Model A-3, made by Nippon Bunko Kogyo Co., for a 75 .mu.m thick film made from the copolymer.